After upgrading to Sourcetree 3.2.6 the push dialog doesn't show the available branches to push

This is happening on a colleague's machine. I can still push to the remote via the command line but not via the SourceTree push dialog. We tried restarting Sourcetree and also restarting the laptop (running Windows 10 x64). I'm running the same version of SourceTree (3.2.6) on my machine without an…